The two main objectives of the project are: Objective 1) To explore the validity of some of the experimental support of the immune surveillance theory, especially (a) the direct effect of the oncogenic agent on the immune response of the host (i.e., the carcinogen as immunodepressant) and (b) the effect of immunosuppression or of genetic defects of the immune system (i.e., nude athymic mice) on tumor development either spontaneous or after exposure to chemical or viral carcinogens. Objective 2) To explore the role of carcinogen-host and of tumor-host interactions on tumor development and tumor progression, especially pertaining to immune functions and tumor immunity. The experimental models to be used are mainly inbred mouse strains that are either susceptible or resistant to the oncogenic action of chemical or viral agents. The genetics of such resistance- susceptibility, as well as the possible role of immune functions on the resistance will also be studied. The two main models used are the resistance of certain mouse strains to methylcholanthrene and other polycyclic hydrocarbons and the resistance of several mouse strains to the oncogenic effect of Friend virus and of some Friend virus variants. These studies will help to understand the role of the host, whether immunological or not, on susceptibility to tumor development in mammals.